The Heart Rate Variability Correlates of Spontaneous Drowsiness Onset 730124

The disturbingly high estimate of single vehicle automobile accidents felt to be drowsiness-related has suggested the need for physiologic or behavioral alertness indicators. This experiment is one phase in the systematic evaluation of the reliability of heart rate variability (HRV) as such an indicator. Nine subjects became spontaneously drowsy in a passive laboratory situation, while heart rate (HR), EEG, and other physiologic measurements were recorded for 1 h. Beat-to-beat heart activity in 40 s of waking record was compared with heart activity in 40 s of adjacent drowsy record, using electrographic definitions of waking and drowsy (transitional) states. Of three descriptors of heart activity, HRV only as measured by the mean square of HR, showed an inverse, but marginally significant and unreliable relationship to drowsiness onset. Neither HR nor HRV measured by mean square of successive differences of HR showed any relationship to drowsiness onset at all. We conclude that HRV is not a reliable predictor of spontaneous drowsiness onset in the passive laboratory situation.